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daemon.py
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#!/usr/bin/env python3
"""Generic linux daemon base class for python 3.x."""
import os
import sys
import time
import atexit
import signal
class daemon:
"""A generic daemon class.
Usage: subclass the daemon class and override the run() method."""
def __init__(self, pidfile):
self.pidfile = pidfile
def daemonize(self):
"""Deamonize class. UNIX double fork mechanism."""
try:
pid = os.fork()
if pid > 0:
# exit first parent
sys.exit(0)
except OSError as err:
sys.stderr.write('fork #1 failed: {0}\n'.format(err))
sys.exit(1)
# decouple from parent environment
os.chdir('/')
os.setsid()
os.umask(0)
# do second fork
try:
pid = os.fork()
if pid > 0:
# exit from second parent
sys.exit(0)
except OSError as err:
sys.stderr.write('fork #2 failed: {0}\n'.format(err))
sys.exit(1)
# redirect standard file descriptors
sys.stdout.flush()
sys.stderr.flush()
si = open(os.devnull, 'r')
so = open(os.devnull, 'a+')
se = open(os.devnull, 'a+')
# write pidfile
atexit.register(self.delpid)
pid = str(os.getpid())
with open(self.pidfile, 'w+') as f:
f.write(pid + '\n')
def delpid(self):
os.remove(self.pidfile)
def start(self):
"""Start the daemon."""
# Check for a pidfile to see if the daemon already runs
try:
with open(self.pidfile, 'r') as pf:
pid = int(pf.read().strip())
except IOError:
pid = None
if pid:
message = "pidfile {0} already exist. " + \
"Daemon already running?\n"
sys.stderr.write(message.format(self.pidfile))
sys.exit(1)
# Start the daemon
self.daemonize()
self.run()
def stop(self):
"""Stop the daemon."""
# Get the pid from the pidfile
try:
with open(self.pidfile, 'r') as pf:
pid = int(pf.read().strip())
except IOError:
pid = None
if not pid:
message = "pidfile {0} does not exist. " + \
"Daemon not running?\n"
sys.stderr.write(message.format(self.pidfile))
return # not an error in a restart
# Try TERMinatting the daemon process
# If that does not work, KILL IT
# TODO: analyze why it doesn't work sometimes.
# must be threading related...
try:
termcounter = 0
while 1:
os.kill(pid, signal.SIGTERM)
time.sleep(0.1)
termcounter += 1
if termcounter == 100:
print("Not response to SIGMTERM. Killing. (FIXME)")
os.kill(pid, signal.SIGKILL)
except OSError as err:
e = str(err.args)
if e.find("No such process") > 0:
if os.path.exists(self.pidfile):
os.remove(self.pidfile)
else:
print(str(err.args))
sys.exit(1)
def restart(self):
"""Restart the daemon."""
self.stop()
self.start()
def run(self):
"""You should override this method when you subclass Daemon.
It will be called after the process has been daemonized by
start() or restart()."""